The present invention pertains to the area of field emission devices and, more particularly, to methods for cleaning and conditioning electron emitters in a field emission device.
A typical field emission device contains electron emitters, such as Spindt tips, which are made from an electron-emissive metal, such as molybdenum. These electron emitters are susceptible to surface contamination by oxygen-containing, sulfur-containing, and carbon-containing species. The surface oxygen and carbon have deleterious effects on the electron emission properties of the electron emitters. In particular, the presence of oxygen and carbon at the emissive surface increases the surface work function of the electron emitters. That is, a larger electric field is required to extract electrons therefrom due to the contamination. Surface contaminants also result in emission current instability and reduced device lifetime.
Metal field emission tips have been employed in field emission electron and ion microscopy, scanning tunneling microscopy, etc. It is known to remove surface contaminants from electron emitters in these microscopy systems by employing high temperature (greater than 2000xc2x0 K) flashing. However, field emission arrays often include glass substrates upon which the electron emitters are formed. These glass substrates have temperature tolerances up to 700-800xc2x0 K. Thus, high temperature cleaning procedures cannot be used for decontaminating field emission electron emitters formed on glass substrates.
It is also known in the art that hydrogen treatment of the electron emitters improves the field emission and leads to higher current. It is believed that one of the main mechanisms of improvement is removal and replacement of surface oxygen by the hydrogen. Once in the surface, the hydrogen acts as a protective layer preventing further oxidation or other chemical contamination of the surface.
However, a problem with this prior art scheme is that field emitted current induces desorption of hydrogen from the surface of the electron emitter. Thus, during the operation of the device, the protective surface hydrogen layer is removed, causing deterioration of the performance and lifetime of the device.
Accordingly, there exists a need for an improved field emission device and method for the conditioning thereof, which overcome at least these shortcomings of the prior art.